Currently cutting is done with linuxcnc. The wood is 4mm thick poplar triplex and I cut at 15mm/s with 100% power on a 80W reci tube and around 400PPI

The cut is ok, but I might be able to reduce charring some more. That will need some experimenting and for that I'll wait until my air assist compressor arrives and my fume extraction (630CFM) arrives.

The demo object is 70x60 mm

I think I'll need to reduce cutting speed and up my PPI settings, but for that any hints/tips are very welcome.

Earlier today I also cut 10x10mm rectangles out of this 4mm thick triplex and the final cut-out rectangle was 9.8x9.8mm, so I really get a very nice 0.2mm (0.0078") kerf.

It looks like you are cutting and marking at the same feed rate but different laser powers? If this is the case you can use the same power for both and just go faster on the engraving. For example I cut 1/8" acrylic at 7 ipm and 40% duty cycle, but I do marking at 60ipm and the same 40% duty cycle. This an example where duty cycle is much easier to control than PPI, just go faster to cut less deep.

Also the rapid movements look very slow. I would expect a laser cutter to be 600-1000 ipm on rapids.

At this moment I haven't upped my rapids for 1 very simple reason. The machine can rapid on Y without problems at +- 1400 IPM and on X it can even go 2350 IPM.

However. Even if the machine is constructed of 35x35mm (1.4"x1.4") aluminium extrusions. When my Y axis moves fast (my acceleration is quite high on this one, at 236inches/sec²) then the whole machine is wobbling.

This is mostly because of 2 reasons:

1) The machine is still in skeleton state. When al electronics , air assist motor and fume extraction are built-in, then there will be a 2mm thick steel plating around the machine which will make the aluminium extrusions a lot more rigid and allow me to go rapids.

2) Because the machine is quite big (machine itself is 63inches long, 47 inches deep and 23.5 inches high) fast movements create a huge amount or inertia. The machine is mounted onto 2 tables and these are only standing on 4 feet.The result is that this table is not that stable and as soon as the machine does rapids, the table begins to wobble too. (I even think that the table wobbles a lot more then the aluminium extrusions, but that is something to find out.) Once I'm ready, I'll mount plates under the table edge so that the table surface will be in full contact with the ground and not only by 4 feet. (40mm MDF plate mounted between table top and ground), you should be able to just press it underneath and it will sit there, blocking the table from wobbling.

So thats the main reason why I don't do rapids now.

The reason why you see burned edges is because I was still experimenting there with PPI settings and the cut you saw is at 100% power, 400PPI but at 35IPM. I reduced that speed to 16IPM and now the result is perfect.

The only problem I still have is rastering. The movie yousaw above is using EMC2 (not 2.5.x) with Ben Jackson config. I can get raster engraving working a little bit there, but not completely and I'm certainly not able to engrave for example 4 pictures in 1 laserjob. The laser engraves the first one, but with the next 3 it does all sweeps with X and Y axis, but nothing is burned onto wood.

So, next step is to format a machine with latest live cd and then try out your way (your config) for raster engraving.

Like I understood it now, with your system everything is in 1 single gcode file. (At least its possible).So for example if I want to engrave a 5"x5" picture (raster engrave) and then cut it out, I could combine the engraving and cutting in 1 single .ngc file and run on linuxcnc with your config ?

That would certainly rock a lot. I don't really care if it would make the gcode file very big, thats my computers problem, not mine

So.... that'll be my next step to see how I can solve raster engraving to get consistent results without having to worry if the laser is going to shoot, or only goint to sweep but nothing shot

The first engraving was a success, but the quality is still not what it should be (which will require some trial and error)

Now I must admit that until now, I haven't yet searched for the exact focal point of my laser. I always place a 1/2" piece between my sheet and laser head to measure that height, but I really don't know if 1/2" is the correct distance. Dure it looks nice, but if its not 100% ok then I'll never find the best possible quality.

So... I'll have to find out a way to find optimal focussing. Ideas are welcome !

If you have a motorized bed you can just move it down as you sweep, then find the smallest spot size and measure where it is in your sweep, then calculate what the W value is, move to that W with G0 W? and now the bed is at the correct height. To keep this distance measure from the laser carriage or nozzle to the top of the work and that is your best focus distance. In this gcode it moves the bed down .5 inches over 10 inches. So if the best focus is at 2 inches into the line, your best W is 0.1. G0 W0.1 and measure.

Be sure to touch off your W axis before running this. Touch off at a point above good focus.

%M4 S100M68 E0 Q20

G20G61G0 X0 Y0 W0

M62 P0G1 X10 W-0.5 F600M63 P0

G0 X0%

Based on your raster picture it looks like you have some slop in your Y axis belt. The first raster line is wavy. Also looks like you can go higher DPI as the black areas are not getting overlapping dots.

I don't know if its SLOP in the Y. I rather think that it is my machine wiggling because of the fast G0 move to start. I'll try to replace the initial G0 move with a much slower G1 move.

The reason I get this is because the whole laser X axis is quite heavy and if I move too fast the whole machine wiggles a little.The motorized bed then has time to wiggle a little too, so thats probably the problem. Also the machine doens't have side plates mounted yet so I guess that will improve stability too.

Thanks for the hint about finding focal. I'll test it out since I have motorized Z table. I believe that in your config that is then the W axis ? what axis number would that be for the parameters in the ini file ?

Another possibility to find focus is to use a slanted piece of wood on the bed and cut a line. Find out where the thinnest line is and measure the distance from the area up to the head or the plate the head is mounted on.